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As the advancement of mobile device technology, there are larger demands for touch display screen which are embedded as a replacement of physical keyboard for inputting data. Devices are appealing to large display panel with touch display screen such as mobile phones, portable video game devices and entertainment tablets. There are challenges to develop thinner and sensitive screen to meet the devices development.
In display industry, capacitive touch sensing is one of the most widely adopted technology, due to its high light transmittance and a broad range of temperature tolerance advantages. Typically, a capacitive touch sensing film consists of two transparent conductive electrodes such as ITO coated polyethylene terephthalate (PET) or glass. The two layers of transparent conductive electrodes are separated by a dielectric layer using optical clear adhesive (OCA). The bottom PET layer is usually placed on top of an insulating layer made of glass or a PMMA for insulation while a protective layer of hard coating is placed on top of the upper PET layer for protection.
When a finger or an object presses onto the sensing film, a differential change in capacitance is generated. However, the aforesaid mentioned structures are complicated, which would not only induce optical reflection loss at the interfaces when there are mismatches on the refractive index but also raise reliability concerns and increase material costs.
For large touch screen applications, ITO conductors suffer from a drawback of relatively high electrical resistance which hamper their performance, better alternatives are sought to replace ITO and that may modify the design of capacitive sensing film.
It is against this background to exclude the OCA in order to achieve a thinner display screen.